add basic DoH system tests

- rename dot to doth, as it now covers both dot and doh.
- merge xot into doth as it's closely related.
- added long-lived key and cert files (expiring 2121).
- add tests with https-get, https-post, http-plain, alternate
  endpoints, and both static and ephemeral TLS configuration.
- incidentally fixed a memory leak in dig that occurred if +https
  was specified more than once.

bin/tests/system/conf.sh.common

@@ -668,7 +668,7 @@ copy_setports() {
     atsign="@"
     sed -e "s/${atsign}PORT${atsign}/${PORT}/g" \
         -e "s/${atsign}TLSPORT${atsign}/${TLSPORT}/g" \
-		-e "s/${atsign}HTTPPORT${atsign}/${HTTPSPORT}/g" \
+		-e "s/${atsign}HTTPPORT${atsign}/${HTTPPORT}/g" \
         -e "s/${atsign}HTTPSPORT${atsign}/${HTTPSPORT}/g" \
         -e "s/${atsign}EXTRAPORT1${atsign}/${EXTRAPORT1}/g" \
         -e "s/${atsign}EXTRAPORT2${atsign}/${EXTRAPORT2}/g" \